1. Field of the Invention
The present invention relates to a fluid pressure apparatus of a fluid pressure cylinder or a fluid changeover valve or the like, and more specifically, concerns a fluid pressure device in which a packing is installed. Such a packing constitutes an improvement to a partitioning member comprising a piston or a spool or the like, which moves in the interior of a slide hole defined in a housing.
2. Description of the Related Art
A fluid pressure cylinder generally includes a piston that moves in an axial direction along the interior of a slide hole formed in a housing. A seal member made of an elastic rubber material is installed in an installation groove, which is formed on the outer circumference of the piston, such that through the seal member, sealing is effected between the inner circumference of the slide hole and the outer circumference of the piston. Further, together with the seal member, a wear ring is provided on the piston. In the case that a transverse load acts in a direction tending to cause misalignment between the axis of the slide hole and the axis of the piston, misalignment of the piston axis is suppressed by the wear ring and the packing is prevented from being pressed against the inner surface of the slide hole too hard to be extremely crushed, while at the same time, the outer circumference of the piston is prevented by the wear ring from coming into contact with the inner circumference of the slide hole. The wear ring is formed in an annular shape, including a cut line in a portion thereof, from a material (e.g., a synthetic resin) having a hardness greater than that of the packing and which is superior in terms of slidability. By means of the cut line, the ring can be opened and installed on the outer circumference of the piston.
As an example of a fluid pressure apparatus having such a wear ring, in Japanese Laid-Open Patent Publication No. 09-072310, there is disclosed a device in which a seal member (o-ring) and a backup ring (wear ring) are installed in parallel in an installation groove on the outer circumference of a piston. Further, in Japanese Laid-Open Patent Publication No. 2003-120602, there is disclosed a device in which a seal member (D ring), which is equipped with a sealing projection on the outer circumference thereof, is installed in an installation groove on the outer circumference of a piston, and together therewith, a backup ring (wear ring) is installed thereon so as to surround the outer circumference of shoulder portions on both sides of the sealing projection of the seal member.
However, in the devices disclosed in Japanese Laid-Open Patent Publication No. 09-072310 and Japanese Laid-Open Patent Publication No. 2003-120602, structures are provided in which wear rings made up from a synthetic resin or a metallic material or the like, which are hard and wherein the thickness thereof is large in the radial direction, are fitted into installation grooves together with the seal members. Therefore, due to the rigidity of such wear rings, installation and mounting of the wear rings is comparatively difficult. In this case, because only a small portion of the outer circumferential side of the wear ring projects outwardly from the installation groove, and because it is necessary for the inner circumferential side of the wear ring, which makes up the major portion thereof, to be engaged within the installation grove by being fitted into the installation groove, the thickness of the wear ring in the radial direction cannot easily be reduced or made thin.